Biomass-derived carbon skeleton modified graphite felt electrode, preparation method and application thereof

Abstract

This application relates to the field of flow battery electrode technology, and discloses a biomass-derived carbon framework modified graphite felt electrode and its preparation method and application. The method involves treating graphite felt in an oxidant system to obtain pretreated graphite felt; then, the pretreated graphite felt, biomass raw materials, and a dispersant are added to an acidic solution and ultrasonically dispersed. Next, an active metal source and a coordinating agent are added, followed by ultrasonic dispersion. A crosslinking agent and a coupling agent are then added, followed by stirring, washing, and drying to obtain crosslinked biomass / metal modified graphite felt. Finally, after preheating at a low temperature, carbonization is performed, followed by washing and drying to obtain biomass-derived carbon framework modified graphite felt for vanadium batteries. Through surface oxidation modification, biomass carbon framework modification, and metal active site loading, the surface wettability, electrocatalytic activity, and specific surface area of ​​the graphite felt can be significantly improved, effectively reducing the polarization of the vanadium ion redox reaction, thus significantly improving voltage efficiency.

Description

Technical Field

[0001] This invention relates to the field of vanadium redox flow battery electrode technology, specifically to a biomass-derived carbon skeleton modified graphite felt electrode and its preparation method and application. Background Technology

[0002] Flow battery technology, especially vanadium redox flow batteries, is considered one of the most promising large-scale energy storage technologies due to its unique advantages such as high safety, long cycle life, modular design for scalability and flexibility, and is of great significance for the substitution of non-renewable energy sources. A vanadium redox flow battery system mainly consists of a stack, electrolyte, and other system control components. The stack, as the core material of the system, accounts for a large proportion, and its core components are electrodes, separators, and bipolar plates. Among these, the electrodes are the electrochemical reaction sites for charging and discharging the battery system, and their electrochemical activity directly determines the charging and discharging efficiency of the stack and the system. As a core component of the flow battery, they can improve its operating power density and reduce energy loss due to charge-discharge cycles.

[0003] Early electrodes were primarily metallic materials, including elemental metals such as gold, lead, and titanium, as well as alloys such as titanium-based platinum and titanium-based iridium oxide. However, their poor electrochemical reversibility and high cost made them unsuitable for large-scale, long-term use. Currently, the mainstream electrode materials are carbon-based, such as glassy carbon, graphite, carbon felt, and graphite felt. However, glassy carbon electrodes suffer from poor reversibility, graphite electrodes are easily etched and damaged, and have a small specific surface area, resulting in high internal resistance and difficulty in effectively improving performance. Carbon fiber materials such as graphite felt and carbon felt also have problems such as low electrochemical activity and poor hydrophilicity, requiring process optimization and bulk modification to improve their performance. Currently used modification processes include high-temperature oxidation, noble metal catalytic modification, and strong acid / base treatment, but these still suffer from complex processes, high energy consumption, and the high cost and scarcity of catalytic materials. Therefore, developing a green, low-cost, mild, and highly stable electrode modification technology remains a key issue that the industry urgently needs to address. Summary of the Invention

[0004] The purpose of this invention is to provide a biomass-derived carbon skeleton modified graphite felt electrode, its preparation method and application, to solve the problems of poor hydrophilicity and low electroactivity of existing graphite felt electrodes.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In the first aspect, a method for preparing a biomass-derived carbon framework modified graphite felt electrode is disclosed, comprising the following steps: Step S1: After cleaning and drying the graphite felt, place it in an oxidant system and continue to treat it at a constant temperature. Then clean and dry it again to obtain pretreated graphite felt. Step S2: Add the pretreated graphite felt, biomass raw materials and dispersant to an acidic solution and perform ultrasonic dispersion treatment. Then add the active metal source and ligand and perform ultrasonic dispersion treatment again to obtain a metal-biomass dispersion. Add a crosslinking agent and coupling agent to the metal-biomass dispersion, stir treatment, take out the graphite felt, wash and dry it to obtain crosslinked biomass-metal modified graphite felt. Step S3: The cross-linked biomass-metal modified graphite felt is transferred to a heat treatment furnace. A mixed gas consisting of carbon dioxide and inert gas is continuously introduced to remove air from the furnace. After preheating at a low temperature, the temperature is raised to the carbonization temperature at a constant rate and held at that temperature. Then, it is naturally cooled to room temperature. The obtained graphite felt is then washed with an acidic cleaning solution and dried to obtain the biomass-derived carbon skeleton modified graphite felt electrode.

[0006] In one implementation, in step S1: The cleaning and drying method is as follows: rinse with deionized water and anhydrous ethanol 3-5 times respectively to remove surface impurities and oil stains, and then vacuum dry at a temperature of 80-120℃ for 6-8 hours.

[0007] The oxidant in the oxidant system is at least two of the following: potassium permanganate solution, dilute sulfuric acid solution, dilute nitric acid solution, ammonium persulfate solution, and hydrogen peroxide solution. The concentration of any one of the oxidants is 1 mol / L, and the oxidant system is formed by mixing at least two oxidants in an equal mass ratio. The continuous treatment at constant temperature lasts for 30-120 minutes, and the temperature is 25-70℃.

[0008] By oxidizing the graphite felt after cleaning, and using a combination of two or more oxidants, oxygen-containing functional groups such as -COOH, -OH, and C=O can be uniformly and gently introduced onto the surface of the graphite felt. This allows for the adjustment of the type and density of functional groups, avoiding uneven oxidation or over-etching by a single oxidant. At the same time, the oxygen-containing functional groups can form strong hydrogen bonds and chemical bonds with various groups in the subsequent biomass molecules, improving the adhesion and stability of the subsequent biomass cross-linking layer on the graphite felt surface, and solving the problem of easy coating peeling and cracking during high-temperature carbonization.

[0009] In one implementation, in step S2: The biomass raw material is one of chitosan, gelatin, carboxymethyl cellulose, cellulose, pectin, and silk fibroin; The dispersant is one of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, polyethylene glycol, sodium polyacrylate, and polyvinyl alcohol; The acidic solution is one of acetic acid solution, formic acid solution, oxalic acid solution, and citric acid solution, and the concentration of the acidic solution is 0.05-0.5 mol / L; The mass ratio of the pretreated graphite felt, biomass raw material, dispersant, and acidic solution is 4:(0.5-2):(0.1-0.5):(200-500).

[0010] In one implementation, in step S2: The active metal source is one of ferric citrate, ferric acetate, ferric chloride, ferric gluconate, and ferric acetylacetone. The ligand is one of disodium ethylenediaminetetraacetate, citric acid, glycine, and urea. The mass ratio of the active metal source, ligand, and acidic solution is (0.05-0.3):(0.01-0.1):200.

[0011] In one implementation, in step S2: The ultrasonic dispersion treatment is performed at a frequency of 30-60 kHz for a duration of 5-25 min. The crosslinking agent is one of glutaraldehyde, genipin, epichlorohydrin (ECH), butanetetracarboxylic acid, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, and N-hydroxysuccinimide. The coupling agent is one of γ-aminopropyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, diaminopropyltriethoxysilane, and isopropyltrioleyloxytitanate; The mass ratio of the metal-biomass dispersion, crosslinking agent, and coupling agent is 200:(0.5-2):(0.1-0.8).

[0012] By ultrasonically dispersing biomass raw materials and dispersants in an acidic solution, the biomass can be fully swollen and uniformly dispersed, effectively improving its dispersion stability in solution. Simultaneously, it fully wets the surface and three-dimensional pores of graphite felt fibers, providing a uniform and firmly bonded precursor substrate for subsequent composite modification. The addition of active metal sources and ligands forms stable complexes, significantly inhibiting metal ion aggregation and segregation, achieving a highly uniform distribution of metal components in the biomass system, laying the structural foundation for the subsequent formation of highly dispersed active sites. Finally, with the assistance of a coupling agent, a crosslinking reaction is carried out on the biomass, enabling the biomass molecules to form a dense and stable three-dimensional porous network structure, firmly anchoring the metal components. Simultaneously, the coupling agent can construct chemical bridges between the carbon fibers and the composite coating, significantly improving the interfacial bonding strength, making the modified layer less prone to detachment and resulting in a more stable structure.

[0013] In one implementation, in step S3: The inert gas is one of argon and helium, the ratio of carbon dioxide to the inert gas is 1:5-10, and the flow rate of the mixed gas is 20-50 ml / min. The preheating temperature at the low temperature is 250-350℃, and the preheating time is 0.5-2h; the heating rate is 2-8℃ / min; the carbonization temperature is 900-1300℃, and the holding time is 2-6h. The acidic cleaning solution is one of dilute hydrochloric acid solution, dilute sulfuric acid solution, citric acid solution, or oxalic acid solution.

[0014] Low-temperature preheating can slowly remove moisture and small molecule impurities from the material, avoiding coating cracking, blistering, or peeling caused by rapid heating, and ensuring the integrity and density of the carbon skeleton structure. Subsequent high-temperature heat treatment with inert gas can efficiently convert biomass precursors into highly graphitized and highly conductive derived carbon layers, significantly improving the overall conductivity of the electrode. At the same time, it can achieve in-situ crystallization and high dispersion of active metal species, forming uniform and fine metal active sites. The introduction of carbon dioxide gas can activate and create pores in-situ during high-temperature heat treatment. Through the reaction and etching of carbon and carbon dioxide, rich micropores and mesopores are formed, significantly increasing the specific surface area and porosity of the electrode material, further optimizing the surface defects and wettability of the carbon material, enhancing the electrode's adsorption and penetration ability to electrolyte, providing more active sites and fast transport channels for vanadium ions, and improving the electrocatalytic activity and rate performance of vanadium batteries.

[0015] Secondly, a biomass-derived carbon framework modified graphite felt electrode is disclosed, which is prepared by the above-mentioned preparation method of biomass-derived carbon framework modified graphite felt electrode.

[0016] In one embodiment, the biomass-derived carbon framework modified graphite felt electrode includes a graphite felt substrate, the surface of which is loaded with a biomass-derived carbon framework, and the biomass-derived carbon framework is doped with active metal sites.

[0017] In one embodiment, the biomass-derived carbon skeleton has a three-dimensional porous network structure on the surface of the graphite felt substrate, and the active metal sites are uniformly dispersed in the biomass-derived carbon skeleton.

[0018] Thirdly, an application of biomass-derived carbon skeleton modified graphite felt is disclosed, in which the biomass-derived carbon skeleton modified graphite felt electrode prepared by the above-described preparation method or the above-described biomass-derived carbon skeleton modified graphite felt electrode is used in an all-vanadium redox flow battery.

[0019] The beneficial effects of this application are as follows: 1. This application uses a combination of various oxidants to oxidize graphite felt, which can gently and uniformly introduce oxygen-containing functional groups such as carboxyl, hydroxyl, and carbonyl groups on its surface, avoiding uneven etching or excessive damage; the oxygen-containing functional groups can form strong hydrogen bonds and chemical bonds with subsequent biomass, significantly improving the adhesion and stability of the cross-linked layer, and effectively solving the problem of easy coating peeling and cracking during high-temperature carbonization.

[0020] 2. The stepwise synergistic process of ultrasonic dispersion, coordination complexation, cross-linking curing and coupling enhancement allows biomass to fully swell and disperse uniformly in an acidic system, fully impregnating the three-dimensional pores of the graphite felt; the active metal source and the coordinating agent form a stable complex, inhibiting the aggregation of metal ions and achieving a highly uniform distribution; the cross-linking agent and the coupling agent work synergistically to construct a dense and stable three-dimensional porous network structure and strengthen the interfacial bonding, making the composite modification layer firm and non-detachable.

[0021] 3. After low-temperature preheating and high-temperature inert atmosphere heat treatment, impurities can be removed and the carbon skeleton can be made dense and intact, converting biomass into a highly conductive derived carbon layer, while realizing in-situ uniform crystallization of metal active sites; the introduction of carbon dioxide can activate and create pores in situ, forming a rich hierarchical pore structure, increasing the specific surface area and defect density, improving electrode wettability, ion transport efficiency and electrocatalytic activity, so that vanadium batteries exhibit better energy efficiency, voltage efficiency and cycle stability. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a method for preparing a biomass-derived carbon framework modified graphite felt electrode.

[0023] Figure 2 This is a SEM image of the biomass-derived carbon framework modified graphite felt electrode prepared in Example 1. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0025] like Figure 1 As shown, a method for preparing a biomass-derived carbon framework modified graphite felt electrode includes the following steps: Step S1: Rinse the graphite felt with deionized water and anhydrous ethanol 3-5 times to remove surface impurities and oil stains. Then, vacuum dry it at 80-120℃ for 6-8 hours. After that, place it in an oxidant system composed of two or more oxidant solutions mixed in equal mass ratio and treat it at a constant temperature of 25-70℃ for 30-120 minutes. Then, wash and dry it again to obtain pretreated graphite felt. The oxidant is one of potassium permanganate solution, dilute sulfuric acid solution, dilute nitric acid solution, ammonium persulfate solution, and hydrogen peroxide solution, with a concentration of 1 mol / L. Step S2: Add the pretreated graphite felt, biomass raw material, and dispersant to an acidic solution and perform ultrasonic dispersion treatment. Then add an active metal source and a coordinating agent, and perform ultrasonic dispersion treatment again to obtain a metal-biomass dispersion. Add a crosslinking agent and a coupling agent to the metal-biomass dispersion, stir, remove the graphite felt, wash and dry it to obtain crosslinked biomass-metal modified graphite felt. The biomass raw material is one of chitosan, gelatin, carboxymethyl cellulose, cellulose, pectin, and silk fibroin. The dispersant is one of polyvinylpyrrolidone, sodium dodecylbenzene sulfonate, polyethylene glycol, sodium polyacrylate, and polyvinyl alcohol. The acidic solution is one of acetic acid solution, formic acid solution, oxalic acid solution, and citric acid solution, with a concentration of 0.05-0.5 mol / L. The mass ratio of the pretreated graphite felt, biomass raw material, dispersant, and acidic solution is 4:(0.5-2):(0.1-0.5):(200-500). The active metal source is one of ferric citrate, ferric acetate, ferric chloride, ferric gluconate, and ferric acetylacetone; the complexing agent is one of disodium ethylenediaminetetraacetate, citric acid, glycine, and urea; the mass ratio of the active metal source, complexing agent, and acidic solution is (0.05-0.3):(0.01-0.1):200. The ultrasonic dispersion treatment is performed at a frequency of 30-60 kHz for 5-25 min. The crosslinking agent is one of glutaraldehyde, genipin, epichlorohydrin (ECH), butanetetracarboxylic acid, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, and N-hydroxysuccinimide. The coupling agent is one of γ-aminopropyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, diaminopropyltriethoxysilane, and isopropyltrioleyloxytitanate. The mass ratio of the metal-biomass dispersion, crosslinking agent, and coupling agent is 200:(0.5-2):(0.1-0.8).

[0026] Step S3: The cross-linked biomass-metal modified graphite felt is transferred to a heat treatment furnace. A mixed gas consisting of carbon dioxide and an inert gas is continuously introduced to expel air from the furnace. After preheating at a low temperature, the temperature is increased to the carbonization temperature at a constant rate and held at that temperature. Then, it is naturally cooled to room temperature. The resulting graphite felt is then washed with an acidic cleaning solution and dried to obtain a biomass-derived carbon skeleton modified graphite felt electrode for vanadium batteries. The inert gas is either argon or helium, the ratio of carbon dioxide to inert gas is 1:5-10, and the mixed gas flow rate is 20-50 ml / min. The low-temperature preheating temperature is 250-350℃, and the preheating time is 0.5-2 h. The heating rate is 2-8℃ / min. The carbonization temperature is 900-1300℃, and the holding time is 2-6 h. The acidic cleaning solution is either dilute hydrochloric acid solution, dilute sulfuric acid solution, citric acid solution, or oxalic acid solution.

[0027] Example 1: The following technical solution is adopted. Step S1: Rinse the graphite felt with deionized water and anhydrous ethanol 3-5 times to remove surface impurities and oil stains, and then place it in a vacuum drying oven and dry it at 80°C for 8 hours; place the dried graphite felt in a 1:1 mixture of potassium permanganate and dilute nitric acid and treat it at 70°C for 30 minutes, and then clean and dry it again to obtain pretreated graphite felt. Step S2: Pretreated graphite felt, carboxymethyl cellulose, and sodium dodecylbenzenesulfonate are added to a 0.3 mol / L formic acid solution, wherein the mass ratio of pretreated graphite felt, carboxymethyl cellulose, sodium dodecylbenzenesulfonate, and formic acid solution is 4:1:0.2:300. The mixture is then ultrasonically dispersed in an ultrasonic bath. Ferric acetate and citric acid are added, and the mixture is stirred again and ultrasonically dispersed once more, wherein the mass ratio of ferric acetate, citric acid, and formic acid solution is 0.1:0.05:200, resulting in a metal-biomass dispersion. Genipin and γ-methacryloyloxypropyltrimethoxysilane are added to the above metal-biomass dispersion. The mass ratio of methacryloyloxypropyltrimethoxysilane was 200:1:0.5, and the mixture was continuously stirred. Then, the graphite felt was taken out and washed with deionized water and anhydrous ethanol. It was then placed in a vacuum drying oven for drying at 80°C for 12 hours to obtain cross-linked biomass-metal modified graphite felt. Step S3: The cross-linked biomass-metal modified graphite felt is transferred to a heat treatment furnace. A mixture of carbon dioxide and argon in a 1:10 ratio is continuously introduced to remove air from the furnace. The flow rate of the mixed gas is 20 mL / min. After preheating at 250℃ for 2 hours, the temperature is increased to 1300℃ at a constant rate of 2℃ / min and held for 2 hours. Then, it is naturally cooled to room temperature. The obtained graphite felt is then washed with dilute sulfuric acid solution and dried to obtain the biomass-derived carbon skeleton modified graphite felt electrode for vanadium batteries.

[0028] like Figure 2 As shown, the surface of the biomass-derived carbon skeleton modified graphite felt electrode prepared in Example 1 is uniformly coated with a carbon layer. After a series of dispersion, coordination complexation, and cross-linking curing processes, biomass can be fully coated on the surface of the graphite felt fibers, completely wetting the three-dimensional pores of the graphite felt. The stable complexation of the active metal source and the ligand can also inhibit the aggregation of metal ions, thereby achieving a highly uniform distribution of active materials. Through the synergistic effect of subsequent cross-linking agents and coupling agents, a dense and stable three-dimensional porous network structure is constructed and the interfacial bonding is strengthened, making the composite modification layer firm and non-detachable. Subsequent staged heat treatment can remove impurities and ensure the dense and complete carbon skeleton, thereby converting biomass into a heteroatom-doped, highly conductive derived carbon layer. The heat treatment with mixed gas forms a rich hierarchical porous structure, increasing the specific surface area and defect density, improving electrode wettability, ion transport efficiency, and electrocatalytic activity, thereby improving the overall performance of vanadium batteries.

[0029] Example 2: The following technical solution is adopted. Step S1: Rinse the graphite felt with deionized water and anhydrous ethanol 3-5 times to remove surface impurities and oil stains, and then place it in a vacuum drying oven and dry it at 90℃ for 7 hours; place the dried graphite felt in a 1:1:1 mixture of dilute sulfuric acid solution + dilute nitric acid + potassium permanganate solution and continue to treat it at 50℃ for 60 minutes, and then clean and dry it again to obtain pretreated graphite felt. Step S2: Pretreated graphite felt, silk fibroin, and polyvinylpyrrolidone were added to a 0.1 mol / L citric acid solution, wherein the mass ratio of pretreated graphite felt, silk fibroin, polyvinylpyrrolidone, and citric acid solution was 4:0.5:0.5:500. The solution was then ultrasonically dispersed in an ultrasonic bath. Ferric gluconate and disodium ethylenediaminetetraacetate were added, and the mixture was stirred again and ultrasonically dispersed once more, wherein the mass ratio of ferric gluconate, disodium ethylenediaminetetraacetate, and citric acid solution was 0.05:0.01:200, resulting in a metal-biomass dispersion. Epichlorohydrin (ECH) and isopropyltrioleoyl oxytitanate were added to a metal-biomass dispersion. The mass ratio of the metal-biomass dispersion, epichlorohydrin (ECH), and isopropyltrioleoyl oxytitanate was 200:0.5:0.1. The mixture was continuously stirred. Afterward, the graphite felt was removed and washed with deionized water and anhydrous ethanol. It was then placed in a vacuum drying oven and dried at 100°C for 10 hours to obtain cross-linked biomass-metal modified graphite felt. Step S3: The cross-linked biomass-metal modified graphite felt is transferred to a heat treatment furnace. A mixture of carbon dioxide and argon in a 1:8 ratio is continuously introduced to remove air from the furnace. The flow rate of the mixed gas is 30 mL / min. After preheating at 250℃ for 1 h, the temperature is increased to 1000℃ at a constant rate of 5℃ / min and held for 4 h. Then, it is naturally cooled to room temperature. The obtained graphite felt is then washed with dilute hydrochloric acid solution and dried to obtain the biomass-derived carbon skeleton modified graphite felt electrode for vanadium batteries.

[0030] Example 3: The following technical solution is adopted. Step S1: Rinse the graphite felt with deionized water and anhydrous ethanol 3-5 times to remove surface impurities and oil stains, and then place it in a vacuum drying oven and dry it at 100℃ for 6 hours; place the dried graphite felt in a 1:1 mixture of potassium permanganate solution and ammonium persulfate solution and treat it at 50℃ for 70 minutes, and then clean and dry it again to obtain pretreated graphite felt. Step S2: Pretreated graphite felt, cellulose, and polyvinyl alcohol are added to a 0.05 mol / L oxalic acid solution, wherein the mass ratio of pretreated graphite felt, cellulose, polyvinyl alcohol, and oxalic acid solution is 4:2:0.1:200. The solution is then ultrasonically dispersed in an ultrasonic bath. Ferric citrate and urea are added, and the mixture is stirred again and ultrasonically dispersed once more, with a mass ratio of ferric citrate, urea, and oxalic acid solution of 0.05:0.1:200, to obtain a metal-biomass dispersion. Glutaraldehyde and diaminopropyltriethoxysilane are added to the metal-biomass dispersion, with a mass ratio of metal-biomass dispersion, glutaraldehyde, and diaminopropyltriethoxysilane of 200:1:0.8, and the mixture is continuously stirred. The graphite felt is then removed and washed with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 120°C for 8 hours to obtain cross-linked biomass-metal modified graphite felt. Step S3: The cross-linked biomass-metal modified graphite felt is transferred to a heat treatment furnace. A mixture of carbon dioxide and argon in a 1:5 ratio is continuously introduced to remove air from the furnace. The flow rate of the mixed gas is 50 mL / min. After preheating at 300℃ for 0.5 h, the temperature is increased to 900℃ at a constant rate of 8℃ / min and held for 6 h. Then, it is naturally cooled to room temperature. The obtained graphite felt is then washed with citric acid solution and dried to obtain the biomass-derived carbon skeleton modified graphite felt electrode for vanadium batteries.

[0031] Example 4: The following technical solution is adopted. Step S1: Rinse the graphite felt with deionized water and anhydrous ethanol 3-5 times to remove surface impurities and oil stains, and then place it in a vacuum drying oven at 110℃ for 6 hours; place the dried graphite felt in a 1:1 mixture of hydrogen peroxide solution and ammonium persulfate solution and treat it at 40℃ for 90 minutes, and then clean and dry it again to obtain pretreated graphite felt. Step S2: Pretreated graphite felt, pectin, and polyethylene glycol are added to a 0.5 mol / L citric acid solution, wherein the mass ratio of pretreated graphite felt, pectin, polyethylene glycol, and citric acid solution is 4:1:0.3:200. The solution is then ultrasonically dispersed in an ultrasonic bath. Subsequently, ferric acetylacetone and disodium ethylenediaminetetraacetate are added, and the mixture is stirred again and ultrasonically dispersed once more, wherein the mass ratio of ferric acetylacetone, disodium ethylenediaminetetraacetate, and citric acid solution is 0.2:0.05:200, resulting in a metal-biomass dispersion. 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide and γ-aminopropyltriethoxysilane are added to the above metal-biomass dispersion. The mass ratio of aminopropyltriethoxysilane was 200:0.5:0.1, and the mixture was continuously stirred. Then, the graphite felt was taken out and washed with deionized water and anhydrous ethanol. It was then placed in a vacuum drying oven for drying at 100℃ for 8 hours to obtain cross-linked biomass / metal modified graphite felt. Step S3: The cross-linked biomass-metal modified graphite felt is transferred to a heat treatment furnace. A mixture of carbon dioxide and helium in a 1:8 ratio is continuously introduced to remove air from the furnace. The flow rate of the mixed gas is 50 mL / min. After preheating at 300℃ for 1.5 h, the temperature is increased to 1000℃ at a constant rate of 5℃ / min and held for 2 h. Then, it is naturally cooled to room temperature. The obtained graphite felt is then washed with oxalic acid solution and dried to obtain the biomass-derived carbon skeleton modified graphite felt electrode for vanadium batteries.

[0032] Example 5: The following technical solution is adopted. Step S1: Rinse the graphite felt with deionized water and anhydrous ethanol 3-5 times to remove surface impurities and oil stains, and then place it in a vacuum drying oven at 120℃ for 7 hours; place the dried graphite felt in a 1:1:1 mixture of hydrogen peroxide solution, potassium permanganate and nitric acid, and treat it at 30℃ for 110 minutes, and then clean and dry it again to obtain pretreated graphite felt. Step S2: Pretreated graphite felt, gelatin, and sodium polyacrylate are added to a 0.1 mol / L oxalic acid solution, wherein the mass ratio of pretreated graphite felt, gelatin, sodium polyacrylate, and oxalic acid solution is 4:0.5:0.4:400. The solution is then ultrasonically dispersed in an ultrasonic bath. Ferric chloride and glycine are added, and the mixture is stirred again and ultrasonically dispersed once more, wherein the mass ratio of ferric chloride, glycine, and oxalic acid solution is 0.3:0.01:200, resulting in a metal-biomass dispersion. Butanetetracarboxylic acid and diaminopropyltriethoxysilane are added to the metal-biomass dispersion. The metal-biomass dispersion, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, and γ- The mass ratio of aminopropyltriethoxysilane was 200:2:0.8, and the mixture was continuously stirred. Then, the graphite felt was taken out and washed with deionized water and anhydrous ethanol. It was then placed in a vacuum drying oven for drying at 120°C for 12 hours to obtain cross-linked biomass-metal modified graphite felt. Step S3: The cross-linked biomass-metal modified graphite felt is transferred to a heat treatment furnace. A mixture of carbon dioxide and helium in a 1:10 ratio is continuously introduced to remove air from the furnace. The flow rate of the mixed gas is 40 mL / min. After preheating at 350℃ for 2 hours, the temperature is increased to 1200℃ at a constant rate of 2℃ / min and held for 5 hours. Then, it is naturally cooled to room temperature. The obtained graphite felt is then washed with citric acid solution and dried to obtain the biomass-derived carbon skeleton modified graphite felt electrode for vanadium batteries.

[0033] Example 6: The following technical solution is adopted. Step S1: Rinse the graphite felt with deionized water and anhydrous ethanol 3-5 times to remove surface impurities and oil stains, and then place it in a vacuum drying oven and dry it at 100℃ for 8 hours; place the dried graphite felt in a 1:1 mixture of sulfuric acid and potassium permanganate solution and treat it at 25℃ for 25 minutes, and then clean and dry it again to obtain pretreated graphite felt. Step S2: Add the pretreated graphite felt, chitosan, and polyvinylpyrrolidone to a concentration of 0.2... In a mol / L acetic acid solution, the pretreated graphite felt, chitosan, polyvinylpyrrolidone, and acetic acid solution were in a mass ratio of 4:1:0.25:500. The solution was then ultrasonically dispersed in an ultrasonic bath. Acetylacetone iron and urea were added, and the mixture was stirred again and ultrasonically dispersed once more. The mass ratio of acetylacetone iron, urea, and acetic acid solution was 0.3:0.05:200, resulting in a metal-biomass dispersion. N-hydroxysuccinimide and isopropyltrioleoyloxytitanate were added to the metal-biomass dispersion. The mass ratio of the metal-biomass dispersion, N-hydroxysuccinimide, and isopropyltrioleoyloxytitanate was 200:0.5:0.5, and the mixture was continuously stirred. The graphite felt was then removed and washed with deionized water and anhydrous ethanol. It was then dried in a vacuum drying oven at 120°C for 8 hours to obtain cross-linked biomass-metal modified graphite felt. Step S3: The cross-linked biomass-metal modified graphite felt is transferred to a heat treatment furnace. A mixture of carbon dioxide and helium in a 1:10 ratio is continuously introduced to remove air from the furnace. The flow rate of the mixed gas is 20 mL / min. After preheating at 350℃ for 2 hours, the temperature is increased to 1300℃ at a constant rate of 8℃ / min and held for 4 hours. Then, it is naturally cooled to room temperature. The obtained graphite felt is then washed with dilute sulfuric acid solution and dried to obtain the biomass-derived carbon skeleton modified graphite felt electrode for vanadium batteries.

[0034] Comparative Example 1: The following technical solution is adopted. Using untreated blank graphite felt Comparative Example 2: The following technical solution is adopted. The only difference from Example 1 is that no active metal source is added. Step S1: Rinse the graphite felt with deionized water and anhydrous ethanol 3-5 times to remove surface impurities and oil stains, and then place it in a vacuum drying oven and dry it at 80°C for 8 hours; place the dried graphite felt in a 1:1 mixture of potassium permanganate and dilute nitric acid and treat it at 70°C for 30 minutes, and then clean and dry it again to obtain pretreated graphite felt. Step S2: Pretreated graphite felt, carboxymethyl cellulose, and sodium dodecylbenzenesulfonate were added to a 0.3 mol / L formic acid solution, wherein the mass ratio of pretreated graphite felt, carboxymethyl cellulose, sodium dodecylbenzenesulfonate, and formic acid solution was 4:1:0.2:300. The solution was then ultrasonically dispersed in an ultrasonic bath. Citric acid was added, and the mixture was stirred again and ultrasonically dispersed once more, with a mass ratio of citric acid to formic acid solution of 0.05:200, to obtain a biomass dispersion. Genipin and γ-methacryloyloxypropyltrimethoxysilane were added to the above biomass dispersion, with a mass ratio of the metal-biomass dispersion, genipin, and γ-methacryloyloxypropyltrimethoxysilane of 200:1:0.5. The mixture was continuously stirred. The graphite felt was then removed and washed with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 80°C for 12 hours to obtain cross-linked biomass-metal modified graphite felt. Step S3: The cross-linked biomass-metal modified graphite felt is transferred to a heat treatment furnace. A mixture of carbon dioxide and argon in a 1:10 ratio is continuously introduced to remove air from the furnace. The flow rate of the mixed gas is 20 mL / min. After preheating at 250℃ for 2 hours, the temperature is increased to 1300℃ at a constant rate of 2℃ / min and held for 2 hours. Then, it is naturally cooled to room temperature. The obtained graphite felt is then washed with dilute sulfuric acid solution and dried to obtain the biomass-derived carbon skeleton modified graphite felt electrode for vanadium batteries.

[0035] Comparative Example 3: The following technical solution is adopted. The only difference from Example 1 is that no crosslinking agent or coupling agent is added. Step S1: Rinse the graphite felt with deionized water and anhydrous ethanol 3-5 times to remove surface impurities and oil stains, and then place it in a vacuum drying oven and dry it at 80°C for 8 hours; place the dried graphite felt in a 1:1 mixture of potassium permanganate and dilute nitric acid and treat it at 70°C for 30 minutes, and then clean and dry it again to obtain pretreated graphite felt. Step S2: Pretreated graphite felt, carboxymethyl cellulose, and sodium dodecylbenzene sulfonate were added to a 0.3 mol / L formic acid solution, wherein the mass ratio of pretreated graphite felt, carboxymethyl cellulose, sodium dodecylbenzene sulfonate, and formic acid solution was 4:1:0.2:300. The solution was placed in an ultrasonic bath for ultrasonic dispersion. Then, ferric acetate and citric acid were added, and the mixture was stirred and ultrasonically dispersed again, wherein the mass ratio of ferric acetate, citric acid, and formic acid solution was 0.1:0.05:200, to obtain a metal-biomass dispersion. The graphite felt was then removed and washed with deionized water and anhydrous ethanol, and then placed in a vacuum drying oven for drying at 80°C for 12 hours to obtain cross-linked biomass-metal modified graphite felt. Step S3: The cross-linked biomass-metal modified graphite felt is transferred to a heat treatment furnace. A mixture of carbon dioxide and argon in a 1:10 ratio is continuously introduced to remove air from the furnace. The flow rate of the mixed gas is 20 mL / min. After preheating at 250℃ for 2 hours, the temperature is increased to 1300℃ at a constant rate of 2℃ / min and held for 2 hours. Then, it is naturally cooled to room temperature. The obtained graphite felt is then washed with dilute sulfuric acid solution and dried to obtain the biomass-derived carbon skeleton modified graphite felt electrode for vanadium batteries.

[0036] Comparative Example 4: The following technical solution is adopted. The only difference from Example 1 is the low-temperature heat treatment. Step S1: Rinse the graphite felt with deionized water and anhydrous ethanol 3-5 times to remove surface impurities and oil stains, and then place it in a vacuum drying oven and dry it at 80°C for 8 hours; place the dried graphite felt in a 1:1 mixture of potassium permanganate and dilute nitric acid and treat it at 70°C for 30 minutes, and then clean and dry it again to obtain pretreated graphite felt. Step S2: Pretreated graphite felt, carboxymethyl cellulose, and sodium dodecylbenzenesulfonate are added to a 0.3 mol / L formic acid solution, wherein the mass ratio of pretreated graphite felt, carboxymethyl cellulose, sodium dodecylbenzenesulfonate, and formic acid solution is 4:1:0.2:300. The mixture is then ultrasonically dispersed in an ultrasonic bath. Ferric acetate and citric acid are added, and the mixture is stirred again and ultrasonically dispersed once more, wherein the mass ratio of ferric acetate, citric acid, and formic acid solution is 0.1:0.05:200, resulting in a metal-biomass dispersion. Genipin and γ-methacryloyloxypropyltrimethoxysilane are added to the above metal-biomass dispersion. The mass ratio of methacryloyloxypropyltrimethoxysilane was 200:1:0.5, and the mixture was continuously stirred. Then, the graphite felt was taken out and washed with deionized water and anhydrous ethanol. It was then placed in a vacuum drying oven for drying at 80°C for 12 hours to obtain cross-linked biomass-metal modified graphite felt. Step S3: The cross-linked biomass-metal modified graphite felt is transferred to a heat treatment furnace. A mixture of carbon dioxide and argon in a 1:10 ratio is continuously introduced to remove air from the furnace. The flow rate of the mixed gas is 20 mL / min. After preheating at 250℃ for 2 hours, the temperature is increased to 600℃ at a constant rate of 2℃ / min and held for 2 hours. Then, it is naturally cooled to room temperature. The obtained graphite felt is then washed with dilute sulfuric acid solution and dried to obtain the biomass-derived carbon skeleton modified graphite felt electrode for vanadium batteries.

[0037] Test method: The graphite felt electrodes obtained in Examples 1-6 and Comparative Examples 1-4 were assembled into small battery stacks as working electrodes and subjected to charge-discharge cycle tests under the same operating conditions. The coulombic efficiency, energy efficiency and voltage efficiency of the battery were recorded. The results are shown in Table 1.

[0038] Table 1 Battery Test Results

[0039] As shown in Table 1, compared to Comparative Example 1, Examples 1-5, through surface oxidation modification, biomass carbon skeleton modification, and metal active site loading, significantly improve the surface wettability, electrocatalytic activity, and specific surface area of ​​the graphite felt, effectively reducing the polarization of the vanadium ion redox reaction, thus significantly improving the voltage efficiency; simultaneously, the electrode reaction kinetics are accelerated and the ion transport resistance is reduced, resulting in a significantly higher battery energy efficiency than the blank graphite felt; from Comparative Example 2, Examples 1-5, by introducing highly dispersed metal active sites, provide efficient catalytic centers for the vanadium ion reaction, greatly accelerating the electrode reaction rate and reducing electrochemical polarization, thereby significantly improving the voltage efficiency; from Comparative Example 3, Examples 1-5, through surface oxidation modification, biomass carbon skeleton modification, and metal active site loading, significantly improve the voltage efficiency; from Comparative Example 3, Examples 1-5, through surface oxidation modification, biomass carbon skeleton modification, and metal active site loading, significantly improve the surface wettability, electrocatalytic activity, and specific surface area of ​​the graphite felt, effectively reducing the polarization of the vanadium ion redox reaction, thus significantly improving the voltage efficiency; from Comparative Example 3, Examples 1-5, through surface oxidation modification, biomass carbon skeleton modification, and metal active site loading, significantly improve .... Examples 1-5 demonstrate how cross-linking and coupling effects strengthen the biomass coating, making its structure more stable and preventing high-temperature carbonization and coating detachment during long-term cycling. This ensures a stable conductive network and catalytic interface, reduces side reactions and internal resistance increases, resulting in more stable voltage efficiency, improved overall battery reversibility, higher energy efficiency, and greater stability during cycling. Furthermore, higher-temperature heat treatment transforms biomass into a highly graphitized derived carbon layer, significantly improving electrode conductivity. It also creates richer pore structures and active sites, reducing ohmic and activation polarization, resulting in a significant improvement in voltage efficiency. The conductive network is more complete, the reaction is more thorough, and internal battery losses are reduced, ultimately effectively improving its energy efficiency.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a biomass-derived carbon framework modified graphite felt electrode, characterized in that, Includes the following steps: Step S1: After cleaning and drying the graphite felt, place it in an oxidant system and continue to treat it at a constant temperature. Then clean and dry it again to obtain pretreated graphite felt. Step S2: The pretreated graphite felt, biomass raw material, and dispersant are added to an acidic solution and ultrasonically dispersed. Then, an active metal source and a complexing agent are added, and ultrasonic dispersion is performed again to obtain a metal-biomass dispersion. A crosslinking agent and a coupling agent are added to the metal-biomass dispersion, and the mixture is stirred. The graphite felt is then removed, washed, and dried to obtain a crosslinked biomass-metal modified graphite felt. The active metal source is one of ferric citrate, ferric acetate, ferric chloride, ferric gluconate, and ferric acetylacetone. The complexing agent is one of disodium ethylenediaminetetraacetate, citric acid, glycine, and urea. The mass ratio of the metal-biomass dispersion, crosslinking agent, and coupling agent is 200:(0.5-2):(0.1-0.8). Step S3: The cross-linked biomass-metal modified graphite felt is transferred to a heat treatment furnace. A mixed gas consisting of carbon dioxide and inert gas is continuously introduced to expel air from the furnace. After preheating at a low temperature, the temperature is increased to the carbonization temperature at a constant rate and held at that temperature. Then, it is naturally cooled to room temperature. The resulting graphite felt is then washed with an acidic cleaning solution and dried to obtain the biomass-derived carbon framework modified graphite felt electrode. The preheating temperature at the low temperature is 250-350℃, and the preheating time is 0.5-2h. The heating rate is 2-8℃ / min. The carbonization temperature is 900-1300℃, and the holding time is 2-6h.

2. The preparation method according to claim 1, characterized in that, In step S1: The cleaning and drying method is as follows: rinse with deionized water and anhydrous ethanol 3-5 times respectively to remove surface impurities and oil stains, and then vacuum dry at a temperature of 80-120℃ for 6-8 hours. The oxidant in the oxidant system is at least two of the following: potassium permanganate solution, dilute sulfuric acid solution, dilute nitric acid solution, ammonium persulfate solution, and hydrogen peroxide solution. The concentration of any one of the oxidants is 1 mol / L, and the oxidant system is formed by mixing at least two oxidants in an equal mass ratio. The continuous treatment at constant temperature lasts for 30-120 minutes, and the temperature is 25-70℃.

3. The preparation method according to claim 1, characterized in that, In step S2: The biomass raw material is one of chitosan, gelatin, carboxymethyl cellulose, cellulose, pectin, and silk fibroin; The dispersant is one of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, polyethylene glycol, sodium polyacrylate, and polyvinyl alcohol; The acidic solution is one of acetic acid solution, formic acid solution, oxalic acid solution, and citric acid solution, and the concentration of the acidic solution is 0.05-0.5 mol / L; The mass ratio of the pretreated graphite felt, biomass raw material, dispersant, and acidic solution is 4:(0.5-2):(0.1-0.5):(200-500).

4. The preparation method according to claim 1, characterized in that, In step S2: The mass ratio of the active metal source, ligand, and acidic solution is (0.05-0.3):(0.01-0.1):

200.

5. The preparation method according to claim 1, characterized in that, In step S2: The ultrasonic dispersion treatment is performed at a frequency of 30-60 kHz for a duration of 5-25 min. The crosslinking agent is one of glutaraldehyde, genipin, epichlorohydrin (ECH), butanetetracarboxylic acid, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, and N-hydroxysuccinimide. The coupling agent is one of γ-aminopropyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, diaminopropyltriethoxysilane, and isopropyltrioleoyloxytitanate.

6. The preparation method according to claim 1, characterized in that, In step S3: The inert gas is one of argon and helium, the ratio of carbon dioxide to the inert gas is 1:5-10, and the flow rate of the mixed gas is 20-50 ml / min. The acidic cleaning solution is one of dilute hydrochloric acid solution, dilute sulfuric acid solution, citric acid solution, or oxalic acid solution.

7. A biomass-derived carbon framework modified graphite felt electrode, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

8. The biomass-derived carbon framework modified graphite felt electrode as described in claim 7, characterized in that, The biomass-derived carbon framework modified graphite felt electrode includes a graphite felt substrate, the surface of which is loaded with a biomass-derived carbon framework, and the biomass-derived carbon framework is doped with active metal sites.

9. The biomass-derived carbon framework modified graphite felt electrode as described in claim 8, characterized in that, The biomass-derived carbon skeleton has a three-dimensional porous network structure on the surface of the graphite felt substrate, and the active metal sites are uniformly dispersed in the biomass-derived carbon skeleton.

10. An application of a biomass-derived carbon framework modified graphite felt electrode, characterized in that, The biomass-derived carbon skeleton modified graphite felt electrode prepared by the preparation method according to any one of claims 1-6 or the biomass-derived carbon skeleton modified graphite felt electrode according to any one of claims 7-9 is used in a vanadium redox flow battery.

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